1. Field of the Invention
The invention relates to a method for regulating the electrical voltage in electrical supply networks and/or consumer units and a device for carrying out said method.
2. Discussion of Background Information
It is generally known to carry out voltage regulation only in the central network nodes of high or medium voltage networks. Further transformation to low-voltage level normally cannot be regulated under load. This network structure is oriented towards the central power supply and has the disadvantage that voltage fluctuations caused by a change in node cannot be adjusted for between the network node and the end consumer. Thus, the exploitable transfer capacity of the network components downstream from the network nodes is limited by the drop in voltage rather than by thermal strength.
Regulating transformers are provided for voltage regulation of the networks in the central network nodes. Regulating transformers are used for incremental voltage regulation in electrical networks by changing the transformer ratio. For this purpose, regulating transformers are fitted with regulating windings with tappings, which can be switched under load. During the switching processes, the load current must not be interrupted and the winding step between the relevant tappings must not be shorted. The second requirement results from the fact that during each switching process between two neighbouring tappings they are necessarily briefly connected to each other due to the first requirement, so that there is a ring current equivalent to the transformer short-circuit current between the switch and the relevant winding, the action of which the transformer is unable to withstand, especially during periodical operation. This transformer short-circuit current is relatively high, since the internal resistance of the transformer is normally small. Furthermore, the incremental switches of the transformers would have to be coordinated with the periodical switching of these high short-circuit currents.
For the above reasons, the switching process in the incremental switch of the transformer does not happen directly but rather in multiple stages, whereby transition impedances are briefly switched into the circuits of the tappings during the switching process, limiting the ring current. In Europe, ohmic transition impedances are common, and in America inductive transition impedances are common. For multi-phase switching, a number of switching principles are applied that are named after the vector diagrams of the switching processes. For example we speak of symmetrical or asymmetrical flag switching.
The disadvantage of the measures used so far to limit the ring current is that they result in complex transition principles and require complex designs of the regulating transformers.